There are a lot of ways to go at dealing with the intermittent nature of wind power (and solar, too). Batteries for storage are one approach, but are too expensive at any large scale right now. Pumped hydro can work, but in pretty limited circumstances. Wider interconnection can also mitigate the problem, but that requires very expensive (and often controversial) new transmission construction.
Then there are the hydrogen-related schemes.
Herten, Germany, plans to use power from a wind plant to electrolyze water to produce hydrogen that will be stored and later used in fuel cells to provide power. And the company Hydrogenics recently said it delivered a project to E.On that will use wind to produce hydrogen by electrolysis, but then the hydrogen will be fed straight into the natural gas system.
The problem there is that you can only add a small amount of hydrogen to the natural gas grid – about 5 percent – without causing problems.
So Audi is taking the idea a step further.
At a plant under development in Werlte, Germany, the company hopes to overcome the limitation of hydrogen by producing it, then reacting it with carbon dioxide to make a knockoff of methane. This “e-gas,” as Audi is calling it, can go directly into the natural gas pipeline without any problems – and it can go into the gas tank of the new Audi natural-gas car due out later this year.
A 25-kilowatt demonstration plant is already operating in Germany, producing synthetic methane. The company behind that demo, SolarFuel, is also doing the Audi plant, which will be a lot bigger, capable of producing enough e-gas “to power 1,500 new Audi A3 Sportback TCNG vehicles 15,000 km (9,320 miles) every year,” according to Audi.
Because the hydrogen is produced from renewable energy sources, and because the CO2 is captured waste from a biogas plant, this is a carbon-neutral “fossil fuel.” So all good? Well, not quite. As Kevin Bullis pointed out in his MIT Technology Review piece on the project, the several-steps nature of this process results in a fair bit of inefficiency. “(W)hen factoring in the losses from burning methane to generate electricity again, the overall process is at best 30 percent efficient,” he writes.
It would be more efficient to put the hydrogen to direct use, but at this point, the infrastructure for natural gas dwarfs that of hydrogen, and Audi is betting this could make synthetic methane more viable.